The only estimate (from exit polls in 28 states) that I've seen is 50% turnout among millennials (in bold halfway down page)
http://civicyouth.org/an-estimated-24-million-young-people-vote-in-2016-election/

Slightly different millennial definition though. Most define it as 18-35, but the results only included 18-29.
Regardless, a significantly higher proportion than 19% of millennials voted in the election.

mustn't forget the social media contribution,
Obama is one tweetin' mother focker .
but it's over now .... and it will never happen again. we will never hear hope and change coming out of the mouth of a candidate again